linux-kernel - Re: [PATCH v2] arm: Fix backtrace generation when IPI is masked

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Message-ID: <20150915134208.GT21084@n2100.arm.linux.org.uk>
Date:	Tue, 15 Sep 2015 14:42:09 +0100
From:	Russell King - ARM Linux <linux@....linux.org.uk>
To:	Daniel Thompson <daniel.thompson@...aro.org>
Cc:	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	patches@...aro.org, linaro-kernel@...ts.linaro.org,
	Thomas Gleixner <tglx@...utronix.de>,
	Hillf Danton <hillf.zj@...baba-inc.com>
Subject: Re: [PATCH v2] arm: Fix backtrace generation when IPI is masked

On Tue, Sep 15, 2015 at 02:15:10PM +0100, Daniel Thompson wrote:
> Actually it already gets masked out. The argument to raise_nmi() points to a
> data structure owned by the backtrace library functions and this structure
> if altered during the execution of nmi_cpu_backtrace() to clear the calling
> CPU.
> 
> I had originally planned to use cpumask_test_and_clear_cpu() for the
> conditional branch but that would be broken because nmi_cpu_backtrace()
> would become a nop if we clear anything from the mask before calling it!
> 
> I guess I should add a comment about this to save us from broken but
> "obviously correct" cleanups in the future...

Absolutely.

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